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none of my bits would touch it to drill it out. i ordered some expensive cobalt bits as recommended by a machinist....they wouldn't much touch it either - had it soaking in oil to keep it cool and cutting.

ended up needing to grind it off with my grinder.

why are these things so hard to drill?

what kind of bits do i buy that can eat through those things next time?

I think they're somewhere in the neighborhood of 10.9 steel (metric equivalent of grade 8),
so that they are the least likely to round off.

Last time I cut a 10.9 bolt it was an 18mm thread and took about 10 minutes of constant cutting with a pneumatic die grinder. VERY hard steel. I can imagine trying to drill it would be nearly impossible without some serious bits and a drill press.

crank shaft bolts, not the torque converter bolts. the TC bolts are easy to drill, because we had to drill one of those too on the same engine. oddly enough my buddy drilled it out using a right handed bit with the drill set on left hand, which i didn't know was possible.

a couple bolts were inordinately tight and the engine had been replaced before - i suppose the previous install was to blame as i've never had trouble with any of those bolts before, they're never rusty or corroded. maybe that's also why the "new" engine went kaboom!?

i doubt i'll use an EZ out again, i'm not sure what word to use to describe the task at hand when one of those shear off, which they easily do.

a 2 and a half foot pipe on my socket wasn't moving it and a 900 ft/lb impact rounded it off, i think it rounded off because it was inordinately tight.

*** given that it had that much force on it - would a welded nut hold? i've done that before but couldn't picture it holding that kind of force. theoretically it should hold if a good weld but practically i don't know that it would. my sloppy mig wire feed might not be up to that task?

If it is just the bolt head that is rounded off try the Craftsman Bolt Out extractor. I personally haven't used them but know of others that have and I have heard of no complaints.

One of the problems with trying to drill them out is that you need to slow the speed of your drill down to where you can watch it revolve when you are drilling hardened parts. Otherwise you are just spinning your wheels

I'll bet anything that the last person in there used locktite. I Had that happen once and it was a major pain to get the bolt to even begin moving. Had to be careful and make sure that we wued a 6 point socket so as not to end up where you are. When I saw the loctite on the bolt I blew a gasket. FEar is one thing, but that was just stupid. I guess they just figured it would be the next guys problem and that guy ended up being me.

Heat is key. It loosens locktite and rust. I never use an EZout without heating the drilled bolt up so it glows before putting the EZout into it. An EZout is weaker than the head the bolt had originally, so if you sheared off the head or rounded it over, the EZout isn't going to work without you heating the bolt up.

With rounded over bolt heads, the first tool I reach for is my welder. By welding a nut to the head of the bolt, you give a new way to grab it with a wrench and you heat the bolt so it's easier to take out.

that's exactly what i did, i got it off no problem. but - i'd like to get left handed drill bits capable of doing this quicker. grinding isn't the fastest thing in the world and being in the rust i see this kind of stuff sometimes (though never on flex plate bolts?).

seems like there has to be good bits that can drill them? i've seen those CNC machines in engineering facilities that can drill anything and immense quantities...aren't there bits out there that will tackle this?

With rounded over bolt heads, the first tool I reach for is my welder.

i do that, but i asked earlier in this thread with no response yet - would a welded on nut hold this much force?

it seems like it should theoretically work but i feel like it would break (i had a 2.5 foot pipe on the socket and it wouldn't budge - it was really tight). my sloppy cheap, wire feed mig welder might not be up to the task? the slag doesn't lend itself to filling in a nice puddle in the nut. i could practice next time.

You had one of the 3 things you needed.A (good?) cobalt bit.You also need the proper slow speed and high feed pressure.An oversped overheated chipped cobalt bit is as useful as a wet noodle.

Cobalt bits vary in quality a lot.I made the mistake of buying a cheapo set.They were inferior to decent HSS bits.Junk.

BTW,cobalt bits are made from solid cobalt steel(not coated) and are as good as new after sharpening,unlike those junky titanium ones thinly coated w/titanium nitride.

I think you mentioned that you were using a cutting fluid, but in case you weren't that's key.

yeah, good quality cobalt, like what you'd get if you ordered from Mcmaster-carr

you could get carbide drills, when you're talking CNC's that will drill anything, they are using carbide drills. They can either be an insert style or just solid carbide. They are expensive though, a set would run somewhere north of $500. You can also get carbide tipped drills that are somewhat more reasonable in price, but still expensive.

you could order a few sizes that you would likely be dealing with. The downside, is that carbide prone to breaking if not run at the proper feed and speed, something very difficult to do when you're talking about hand drills.